Magneto-caloric thermal diode assembly

ABSTRACT

A magneto-caloric thermal diode assembly includes a plurality of thermal stages stacked along an axial direction between a cold side and a hot side. A plurality of magnets is distributed along a circumferential direction within a non-magnetic ring in each of the plurality of thermal stages. Each of the plurality of thermal stages between a cold side thermal stage and a hot side thermal stage is positioned between a respective pair of the plurality of thermal stages along the axial direction. The plurality of magnets of each of the plurality of thermal stages between the cold side thermal stage and the hot side thermal stage is spaced from the non-magnetic ring of one of the respective pair of the plurality of thermal stages along the axial direction and is in conductive thermal contact with the non-magnetic ring of the other of the respective pair of the plurality of thermal stages.

FIELD OF THE INVENTION

The present subject matter relates generally to heat pumps, such asmagneto-caloric heat pumps.

BACKGROUND OF THE INVENTION

Conventional refrigeration technology typically utilizes a heat pumpthat relies on compression and expansion of a fluid refrigerant toreceive and reject heat in a cyclic manner so as to effect a desiredtemperature change or transfer heat energy from one location to another.This cycle can be used to receive heat from a refrigeration compartmentand reject such heat to the environment or a location that is externalto the compartment. Other applications include air conditioning ofresidential or commercial structures. A variety of different fluidrefrigerants have been developed that can be used with the heat pump insuch systems.

While improvements have been made to such heat pump systems that rely onthe compression of fluid refrigerant, at best such can still onlyoperate at about forty-five percent or less of the maximum theoreticalCarnot cycle efficiency. Also, some fluid refrigerants have beendiscontinued due to environmental concerns. The range of ambienttemperatures over which certain refrigerant-based systems can operatemay be impractical for certain locations. Other challenges with heatpumps that use a fluid refrigerant exist as well.

Magneto-caloric materials (MCMs), i.e. materials that exhibit themagneto-caloric effect, provide a potential alternative to fluidrefrigerants for heat pump applications. In general, the magneticmoments of MCMs become more ordered under an increasing, externallyapplied magnetic field and cause the MCMs to generate heat. Conversely,decreasing the externally applied magnetic field allows the magneticmoments of the MCMs to become more disordered and allow the MCMs toabsorb heat. Some MCMs exhibit the opposite behavior, i.e. generatingheat when the magnetic field is removed (which are sometimes referred toas para-magneto-caloric material but both types are referred tocollectively herein as magneto-caloric material or MCM). The theoreticalCarnot cycle efficiency of a refrigeration cycle based on an MCMs can besignificantly higher than for a comparable refrigeration cycle based ona fluid refrigerant. As such, a heat pump system that can effectivelyuse an MCM would be useful.

Challenges exist to the practical and cost competitive use of an MCM,however. In addition to the development of suitable MCMs, equipment thatcan attractively utilize an MCM is still needed. Currently proposedequipment may require relatively large and expensive magnets, may beimpractical for use in e.g., appliance refrigeration, and may nototherwise operate with enough efficiency to justify capital cost.

Accordingly, a heat pump system that can address certain challenges,such as those identified above, would be useful. Such a heat pump systemthat can also be used in a refrigerator appliance would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be apparent from the description, or maybe learned through practice of the invention.

In a first example embodiment, a magneto-caloric thermal diode assemblyincludes a magneto-caloric cylinder. A plurality of thermal stages isstacked along an axial direction between a cold side and a hot side. Acold side thermal stage of the plurality of thermal stages is positionedat the cold side, and a hot side thermal stage of the plurality ofthermal stages is positioned at the hot side. Each of the plurality ofthermal stages includes a plurality of magnets and a non-magnetic ring.The plurality of magnets is distributed along a circumferentialdirection within the non-magnetic ring in each of the plurality ofthermal stages. The plurality of thermal stages and the magneto-caloriccylinder are configured for relative rotation between the plurality ofthermal stages and the magneto-caloric cylinder. Each of the pluralityof thermal stages between the cold side thermal stage and the hot sidethermal stage is positioned between a respective pair of the pluralityof thermal stages along the axial direction. One of the respective pairof the plurality of thermal stages is positioned closer to the cold sidealong the axial direction, and the other of the respective pair of theplurality of thermal stages is positioned closer to the hot side alongthe axial direction. The plurality of magnets of each of the pluralityof thermal stages between the cold side thermal stage and the hot sidethermal stage is spaced from the non-magnetic ring of the one of therespective pair of the plurality of thermal stages along the axialdirection. The plurality of magnets of each of the plurality of thermalstages between the cold side thermal stage and the hot side thermalstage is in conductive thermal contact with the non-magnetic ring of theother of the respective pair of the plurality of thermal stages.

In a second example embodiment, a magneto-caloric thermal diode assemblyincludes a plurality of thermal stages stacked along an axial directionbetween a cold side and a hot side. A cold side thermal stage of theplurality of thermal stages is positioned at the cold side, and a hotside thermal stage of the plurality of thermal stages is positioned atthe hot side. Each of the plurality of thermal stages includes aplurality of magnets and a non-magnetic ring. The plurality of magnetsis distributed along a circumferential direction within the non-magneticring in each of the plurality of thermal stages. Each of the pluralityof thermal stages between the cold side thermal stage and the hot sidethermal stage is positioned between a respective pair of the pluralityof thermal stages along the axial direction. One of the respective pairof the plurality of thermal stages is positioned closer to the cold sidealong the axial direction, and the other of the respective pair of theplurality of thermal stages is positioned closer to the hot side alongthe axial direction. The plurality of magnets of each of the pluralityof thermal stages between the cold side thermal stage and the hot sidethermal stage is spaced from the non-magnetic ring of the one of therespective pair of the plurality of thermal stages along the axialdirection. The plurality of magnets of each of the plurality of thermalstages between the cold side thermal stage and the hot side thermalstage is in conductive thermal contact with the non-magnetic ring of theother of the respective pair of the plurality of thermal stages.

In a second example embodiment, a magneto-caloric thermal diode assemblyincludes a magneto-caloric cylinder. A plurality of thermal stages isstacked along an axial direction between a cold side and a hot side. Acold side thermal stage of the plurality of thermal stages is positionedat the cold side, and a hot side thermal stage of the plurality ofthermal stages is positioned at the hot side. Each of the plurality ofthermal stages includes a plurality of non-magnetic blocks and amagnetic ring. The plurality of non-magnetic blocks is distributed alonga circumferential direction within the magnetic ring in each of theplurality of thermal stages. The plurality of thermal stages and themagneto-caloric cylinder are configured for relative rotation betweenthe plurality of thermal stages and the magneto-caloric cylinder. Eachof the plurality of thermal stages between the cold side thermal stageand the hot side thermal stage is positioned between a respective pairof the plurality of thermal stages along the axial direction. One of therespective pair of the plurality of thermal stages is positioned closerto the cold side along the axial direction. The other of the respectivepair of the plurality of thermal stages is positioned closer to the hotside along the axial direction. The plurality of non-magnetic blocks ofeach of the plurality of thermal stages between the cold side thermalstage and the hot side thermal stage is spaced from the magnetic ring ofthe one of the respective pair of the plurality of thermal stages alongthe axial direction. The plurality of non-magnetic blocks of each of theplurality of thermal stages between the cold side thermal stage and thehot side thermal stage is in conductive thermal contact with themagnetic ring of the other of the respective pair of the plurality ofthermal stages.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures.

FIG. 1 is a refrigerator appliance in accordance with an exampleembodiment of the present disclosure.

FIG. 2 is a schematic illustration of certain components of a heat pumpsystem positioned in the example refrigerator appliance of FIG. 1.

FIG. 3 is a perspective view of a magneto-caloric thermal diodeaccording to an example embodiment of the present subject matter.

FIG. 4 is a section view of the example magneto-caloric thermal diode ofFIG. 3.

FIG. 5 is a perspective view of the example magneto-caloric thermaldiode of FIG. 3 with certain thermal stages removed from the examplemagneto-caloric thermal diode.

FIG. 6 is a section view of the example magneto-caloric thermal diode ofFIG. 5.

FIG. 7 is a perspective view of the example magneto-caloric thermaldiode of FIG. 5 with an insulation layer removed from the examplemagneto-caloric thermal diode.

FIG. 8 is a schematic view of the certain components of the examplemagneto-caloric thermal diode of FIG. 3.

FIG. 9 is a schematic view of the certain components of amagneto-caloric thermal diode according to another example embodiment ofthe present subject matter.

FIG. 10 is a schematic view of the certain components of amagneto-caloric thermal diode according to an additional exampleembodiment of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Referring now to FIG. 1, an exemplary embodiment of a refrigeratorappliance 10 is depicted as an upright refrigerator having a cabinet orcasing 12 that defines a number of internal storage compartments orchilled chambers. In particular, refrigerator appliance 10 includesupper fresh-food compartments 14 having doors 16 and lower freezercompartment 18 having upper drawer 20 and lower drawer 22. Drawers 20,22 are “pull-out” type drawers in that they can be manually moved intoand out of freezer compartment 18 on suitable slide mechanisms.Refrigerator 10 is provided by way of example only. Other configurationsfor a refrigerator appliance may be used as well including applianceswith only freezer compartments, only chilled compartments, or othercombinations thereof different from that shown in FIG. 1. In addition,the magneto-caloric thermal diode and heat pump system of the presentdisclosure is not limited to refrigerator appliances and may be used inother applications as well such as e.g., air-conditioning, electronicscooling devices, and others. Thus, it should be understood that whilethe use of a magneto-caloric thermal diode and heat pump system toprovide cooling within a refrigerator is provided by way of exampleherein, the present disclosure may also be used to provide for heatingapplications as well.

FIG. 2 is a schematic view of various components of refrigeratorappliance 10, including refrigeration compartments 30 (e.g., fresh-foodcompartments 14 and freezer compartment 18) and a machinery compartment40. Refrigeration compartment 30 and machinery compartment 40 include aheat pump system 52 having a first or cold side heat exchanger 32positioned in refrigeration compartment 30 for the removal of heattherefrom. A heat transfer fluid such as e.g., an aqueous solution,flowing within cold side heat exchanger 32 receives heat fromrefrigeration compartment 30 thereby cooling contents of refrigerationcompartment 30.

The heat transfer fluid flows out of cold side heat exchanger 32 by line44 to magneto-caloric thermal diode 100. As will be further describedherein, the heat transfer fluid rejects heat to magneto-caloric material(MCM) in magneto-caloric thermal diode 100. The now colder heat transferfluid flows by line 46 to cold side heat exchanger 32 to receive heatfrom refrigeration compartment 30.

Another heat transfer fluid carries heat from the MCM in magneto-caloricthermal diode 100 by line 48 to second or hot side heat exchanger 34.Heat is released to the environment, machinery compartment 40, and/orother location external to refrigeration compartment 30 using secondheat exchanger 34. From second heat exchanger 34, the heat transferfluid returns by line 50 to magneto-caloric thermal diode 100. The abovedescribed cycle may be repeated to suitable cool refrigerationcompartment 30. A fan 36 may be used to create a flow of air acrosssecond heat exchanger 34 and thereby improve the rate of heat transferto the environment.

A pump or pumps (not shown) cause the heat transfer fluid to recirculatein heat pump system 52. Motor 28 is in mechanical communication withmagneto-caloric thermal diode 100 and is operable to provide relativemotion between magnets and a magneto-caloric material of magneto-caloricthermal diode 100, as discussed in greater detail below.

Heat pump system 52 is provided by way of example only. Otherconfigurations of heat pump system 52 may be used as well. For example,lines 44, 46, 48, and 50 provide fluid communication between the variouscomponents of heat pump system 52 but other heat transfer fluidrecirculation loops with different lines and connections may also beemployed. Still other configurations of heat pump system 52 may be usedas well.

In certain exemplary embodiments, cold side heat exchanger 32 is theonly heat exchanger within heat pump system 52 that is configured tocool refrigeration compartments 30. Thus, cold side heat exchanger 32may be the only heat exchanger within cabinet 12 for cooling fresh-foodcompartments 14 and freezer compartment 18. Refrigerator appliance 10also includes features for regulating air flow across cold side heatexchanger 32 and to fresh-food compartments 14 and freezer compartment18.

As may be seen in FIG. 2, cold side heat exchanger 32 is positionedwithin a heat exchanger compartment 60 that is defined within cabinet12, e.g., between fresh-food compartments 14 and freezer compartment 18.Fresh-food compartment 14 is contiguous with heat exchanger compartment60 through a fresh food duct 62. Thus, air may flow between fresh-foodcompartment 14 and heat exchanger compartment 60 via fresh food duct 62.Freezer compartment 18 is contiguous with heat exchanger compartment 60through a freezer duct 64. Thus, air may flow between freezercompartment 18 and heat exchanger compartment 60 via freezer duct 64.

Refrigerator appliance 10 also includes a fresh food fan 66 and afreezer fan 68. Fresh food fan 66 may be positioned at or within freshfood duct 62. Fresh food fan 66 is operable to force air flow betweenfresh-food compartment 14 and heat exchanger compartment 60 throughfresh food duct 62. Fresh food fan 66 may thus be used to create a flowof air across cold side heat exchanger 32 and thereby improve the rateof heat transfer to air within fresh food duct 62. Freezer fan 68 may bepositioned at or within freezer duct 64. Freezer fan 68 is operable toforce air flow between freezer compartment 18 and heat exchangercompartment 60 through freezer duct 64. Freezer fan 68 may thus be usedto create a flow of air across cold side heat exchanger 32 and therebyimprove the rate of heat transfer to air within freezer duct 64.

Refrigerator appliance 10 may also include a fresh food damper 70 and afreezer damper 72. Fresh food damper 70 is positioned at or within freshfood duct 62 and is operable to restrict air flow through fresh foodduct 62. For example, when fresh food damper 70 is closed, fresh fooddamper 70 blocks air flow through fresh food duct 62, e.g., and thusbetween fresh-food compartment 14 and heat exchanger compartment 60.Freezer damper 72 is positioned at or within freezer duct 64 and isoperable to restrict air flow through freezer duct 64. For example, whenfreezer damper 72 is closed, freezer damper 72 blocks air flow throughfreezer duct 64, e.g., and thus between freezer compartment 18 and heatexchanger compartment 60. It will be understood that the positions offans 66, 68 and dampers 70, 72 may be switched in alternative exemplaryembodiments.

Operation of heat pump system 52 and fresh food fan 66 while fresh fooddamper 70 is open, allows chilled air from cold side heat exchanger 32to cool fresh-food compartment 14, e.g., to about forty degreesFahrenheit (40° F.). Similarly, operation of heat pump system 52 andfreezer fan 68 while freezer damper 72 is open, allows chilled air fromcold side heat exchanger 32 to cool freezer compartment 18, e.g., toabout negative ten degrees Fahrenheit (−10° F.). Thus, cold side heatexchanger 32 may chill either fresh-food compartment 14 or freezercompartment 18 during operation of heat pump system 52. In such amanner, both fresh-food compartments 14 and freezer compartment 18 maybe air cooled with cold side heat exchanger 32.

FIGS. 3 through 8 are various views of magneto-caloric thermal diode 200according to an example embodiment of the present subject matter.Magneto-caloric thermal diode 200 may be used in any suitable heat pumpsystem. For example, magneto-caloric thermal diode 200 may be used inheat pump system 52 (FIG. 2). As discussed in greater detail below,magneto-caloric thermal diode 200 includes features for transferringthermal energy from a cold side 202 of magneto-caloric thermal diode 200to a hot side 204 of magneto-caloric thermal diode 200. Magneto-caloricthermal diode 200 defines an axial direction A, a radial direction R anda circumferential direction C.

Magneto-caloric thermal diode 200 includes a plurality of thermal stages210. Thermal stages 210 are stacked along the axial direction A betweencold side 202 and hot side 204 of magneto-caloric thermal diode 200. Acold side thermal stage 212 of thermal stages 210 is positioned at coldside 202 of magneto-caloric thermal diode 200, and a hot side thermalstage 214 of thermal stages 210 is positioned at hot side 204 ofmagneto-caloric thermal diode 200.

Magneto-caloric thermal diode 200 also includes a magneto-caloriccylinder 220 (FIG. 8). In certain example embodiments, thermal stages210 define a cylindrical slot 211, and magneto-caloric cylinder 220 ispositioned within cylindrical slot 211. Thus, e.g., each thermal stage210 may include an inner section 206 and an outer section 208 that arespaced from each other along the radial direction R by cylindrical slot211 such that magneto-caloric cylinder 220 is positioned between innerand outer sections 206, 208 of thermal stages 210 along the radialdirection R. Thermal stages 210 and magneto-caloric cylinder 220 areconfigured for relative rotation between thermal stages 210 andmagneto-caloric cylinder 220. Thermal stages 210 and magneto-caloriccylinder 220 may be configured for relative rotation about an axis Xthat is parallel to the axial direction A. As an example,magneto-caloric cylinder 220 may be coupled to motor 26 such thatmagneto-caloric cylinder 220 is rotatable relative to thermal stages 210about the axis X within cylindrical slot 211 with motor 26. Inalternative exemplary embodiments, thermal stages 210 may be coupled tomotor 26 such that thermal stages 210 are rotatable relative tomagneto-caloric cylinder 220 about the axis X with motor 26.

During relative rotation between thermal stages 210 and magneto-caloriccylinder 220, magneto-caloric thermal diode 200 transfers heat from coldside 202 to hot side 204 of magneto-caloric thermal diode 200. Inparticular, during relative rotation between thermal stages 210 andmagneto-caloric cylinder 220, cold side thermal stage 212 may absorbheat from fresh-food compartments 14 and/or freezer compartment 18, andhot side thermal stage 214 may reject heat to the ambient atmosphereabout refrigerator appliance 10.

Each of the thermal stages 210 includes a plurality of magnets 230 and anon-magnetic ring 240. Magnets 230 are distributed along thecircumferential direction C within non-magnetic ring 240 in each thermalstage 210. In particular, magnets 230 may be spaced from non-magneticring 240 along the radial direction R and the circumferential directionC within each thermal stage 210. For example, each of the thermal stages210 may include insulation 232, and insulation 232 may be positionedbetween magnets 230 and non-magnetic ring 240 along the radial directionR and the circumferential direction C within each thermal stage 210.Insulation 232 may limit conductive heat transfer between magnets 230and non-magnetic ring 240 within each thermal stage 210. As anotherexample, magnets 230 may be spaced from non-magnetic ring 240 along theradial direction R and the circumferential direction C by a gap withineach thermal stage 210. The gap between magnets 230 and non-magneticring 240 within each thermal stage 210 may limit or prevent conductiveheat transfer between magnets 230 and non-magnetic ring 240 within eachthermal stage 210.

It will be understood that the arrangement magnets 230 and non-magneticring 240 may be flipped in alternative example embodiments. Thus, e.g.,a steel and magnet ring may be thermally separate from non-magneticblocks, e.g., aluminum blocks, within each thermal stage 210. Operationmagneto-caloric thermal diode 200 is the same in such configuration.

As may be seen from the above, thermal stages 210 may include featuresfor limiting heat transfer along the radial direction R and thecircumferential direction C within each thermal stage 210. Conversely,thermal stages 210 may be arranged to provide a flow path for thermalenergy along the axial direction A from cold side 202 to hot side 204 ofmagneto-caloric thermal diode 200. Such arrangement of thermal stages210 is discussed in greater detail below.

As noted above, thermal stages 210 includes cold side thermal stage 212at cold side 202 of magneto-caloric thermal diode 200 and hot sidethermal stage 214 at hot side 204 of magneto-caloric thermal diode 200.Thus, cold side thermal stage 212 and hot side thermal stage 214 maycorrespond to the terminal ends of the stack of thermal stages 210. Inparticular, cold side thermal stage 212 and hot side thermal stage 214may be positioned opposite each other along the axial direction A on thestack of thermal stages 210. The other thermal stages 210 are positionedbetween cold side thermal stage 212 and hot side thermal stage 214 alongthe axial direction A. Thus, e.g., interior thermal stages 216 (i.e.,the thermal stages 210 other than cold side thermal stage 212 and hotside thermal stage 214) are positioned between cold side thermal stage212 and hot side thermal stage 214 along the axial direction A.

Each of the interior thermal stages 216 is positioned between arespective pair of thermal stages 210 along the axial direction A. Oneof the respective pair of thermal stages 210 is positioned closer tocold side 202 along the axial direction A, and the other of therespective pair of thermal stages 210 is positioned closer to hot side204 along the axial direction A. For example, a first one 217 ofinterior thermal stages 216 is positioned between hot side thermal stage214 and a second one 218 of interior thermal stages 216 along the axialdirection A. Similarly, second one 218 of interior thermal stages 216 ispositioned between first one 217 of interior thermal stages 216 and athird one 219 of interior thermal stages 216 along the axial directionA.

Each of the interior thermal stages 216 is arranged to provide a flowpath for thermal energy along the axial direction A from cold sidethermal stage 212 to hot side thermal stage 214. In particular, magnets230 of each of interior thermal stages 216 may be spaced fromnon-magnetic ring 240 of the one of the respective pair of thermalstages 210 along the axial direction A. Thus, e.g., magnets 230 of firstone 217 of interior thermal stages 216 may be spaced from non-magneticring 240 of second one 218 of interior thermal stages 216 along theaxial direction A. Similarly, magnets 230 of second one 218 of interiorthermal stages 216 may be spaced from non-magnetic ring 240 of third one219 of interior thermal stages 216 along the axial direction A. Hot sidethermal stage 214 may also be arranged in such a manner.

By spacing magnets 230 of each of interior thermal stages 216 fromnon-magnetic ring 240 of the one of the respective pair of thermalstages 210 along the axial direction A, conductive heat transfer alongthe axial direction A from magnets 230 of each of interior thermalstages 216 to non-magnetic ring 240 of an adjacent one of thermal stages210 towards cold side 202 along the axial direction A may be limited orprevented. In certain example embodiments, magneto-caloric thermal diode200 may include insulation 250. Magnets 230 of each of interior thermalstages 216 may be spaced from non-magnetic ring 240 of the one of therespective pair of thermal stages 210 along the axial direction A byinsulation 250. Insulation 250 may limit conductive heat transfer alongthe axial direction A from magnets 230 of each of interior thermalstages 216 to non-magnetic ring 240 of an adjacent one of thermal stages210 towards cold side 202 along the axial direction A.

Magnets 230 of each of interior thermal stages 216 may also be inconductive thermal contact with non-magnetic ring 240 of the other ofthe respective pair of thermal stages 210. Thus, e.g., magnets 230 offirst one 217 of interior thermal stages 216 may be in conductivethermal contact with non-magnetic ring 240 of hot side thermal stage214. Similarly, magnets 230 of second one 218 of interior thermal stages216 may be in conductive thermal contact with non-magnetic ring 240 offirst one 217 of interior thermal stages 216. Cold side thermal stage212 may also be arranged in such a manner.

By placing magnets 230 of each of interior thermal stages 216 inconductive thermal contact with non-magnetic ring 240 of the other ofthe respective pair of thermal stages 210, thermal energy flow along theaxial direction A towards hot side 204 may be facilitated, e.g.,relative to towards cold side 202. In certain example embodiments,magnets 230 of each of interior thermal stages 216 may be positioned todirectly contact non-magnetic ring 240 of the other of the respectivepair of thermal stages 210. For example, non-magnetic ring 240 of theother of the respective pair of thermal stages 210 may includeprojections 242 that extend along the axial direction A to magnets 230of each of interior thermal stages 216.

The above described arrangement of thermal stages 210 may provide a flowpath for thermal energy along the axial direction A from cold side 202to hot side 204 of magneto-caloric thermal diode 200 during relativerotation between thermal stages 210 and magneto-caloric cylinder 220.Operation of magneto-caloric thermal diode 200 to transfer thermalenergy along the axial direction A from cold side 202 to hot side 204 ofmagneto-caloric thermal diode 200 will now be described in greaterdetail below.

Magnets 230 of thermal stages 210 produce a magnetic field. Conversely,non-magnetic rings 240 do not produce a magnetic field or produce anegligible magnetic field relative to magnets 230. Thus, each of themagnets 230 may correspond to a high magnetic field zone, and theportion of non-magnetic rings 240 between magnets 230 along thecircumferential direction C within each thermal stage 210 may correspondto a low magnetic field zone. During relative rotation between thermalstages 210 and magneto-caloric cylinder 220, magneto-caloric cylinder220 may be sequentially exposed to the high magnetic field zone atmagnets 230 and the low magnetic field zone at non-magnetic rings 240.

Magneto-caloric cylinder 220 includes a magneto-caloric material thatexhibits the magneto-caloric effect, e.g., when exposed to the magneticfield from magnets 230 of thermal stages 210. The caloric material maybe constructed from a single magneto-caloric material or may includemultiple different magneto-caloric materials. By way of example,refrigerator appliance 10 may be used in an application where theambient temperature changes over a substantial range. However, aspecific magneto-caloric material may exhibit the magneto-caloric effectover only a much narrower temperature range. As such, it may bedesirable to use a variety of magneto-caloric materials withinmagneto-caloric cylinder 220 to accommodate the wide range of ambienttemperatures over which refrigerator appliance 10 and/or magneto-caloricthermal diode 200 may be used.

Accordingly, magneto-caloric cylinder 220 can be provided with zones ofdifferent magneto-caloric materials. Each such zone may include amagneto-caloric material that exhibits the magneto-caloric effect at adifferent temperature or a different temperature range than an adjacentzone along the axial direction A of magneto-caloric cylinder 220. Byconfiguring the appropriate number sequence of zones of magneto-caloricmaterial, magneto-caloric thermal diode 200 can be operated over asubstantial range of ambient temperatures.

As noted above, magneto-caloric cylinder 220 includes magneto-caloricmaterial that exhibits the magneto-caloric effect. During relativerotation between thermal stages 210 and magneto-caloric cylinder 220,the magneto-caloric material in magneto-caloric cylinder 220 issequentially exposed to the high magnetic field zone at magnets 230 andthe low magnetic field zone at non-magnetic rings 240. When themagneto-caloric material in magneto-caloric cylinder 220 is exposed tothe high magnetic field zone at magnets 230, the magnetic field causesthe magnetic moments of the magneto-caloric material in magneto-caloriccylinder 220 to orient and to increase (or alternatively decrease) intemperature such that the magneto-caloric material in magneto-caloriccylinder 220 rejects heat to magnets 230. Conversely, when themagneto-caloric material in magneto-caloric cylinder 220 is exposed tothe low magnetic field zone at non-magnetic rings 240, the decreasedmagnetic field causes the magnetic moments of the magneto-caloricmaterial in magneto-caloric cylinder 220 to disorient and to decrease(or alternatively increase) in temperature such that the magneto-caloricmaterial in magneto-caloric cylinder 220 absorbs heat from non-magneticrings 240. By rotating through the high and low magnetic field zones,magneto-caloric cylinder 220 may transfer thermal energy along the axialdirection A from cold side 202 to hot side 204 of magneto-caloricthermal diode 200 by utilizing the magneto-caloric effect of themagneto-caloric material in magneto-caloric cylinder 220.

As noted above, the high magnetic field zones at magnets 230 in each ofthermal stages 210 (e.g., other than hot side thermal stage 214) is inconductive thermal contact with the low magnetic field zone at thenon-magnetic ring 240 of an adjacent thermal stages 210 in the directionof hot side 204 along the axial direction A. Thus, the non-magnetic ring240 of the adjacent thermal stages 210 in the direction of hot side 204may absorb heat from the high magnetic field zones at magnets 230 ineach of thermal stages 210. Thus, thermal stages 210 are arranged toencourage thermal energy flow through thermal stages 210 from cold side202 towards hot side 204 along the axial direction A during relativerotation between thermal stages 210 and magneto-caloric cylinder 220.

Conversely, the high magnetic field zones at magnets 230 in each ofthermal stages 210 (e.g., other than cold side thermal stage 212) isspaced from the low magnetic field zone at the non-magnetic ring 240 ofan adjacent thermal stages 210 in the direction of cold side 202 alongthe axial direction A. Thus, the non-magnetic ring 240 of the adjacentthermal stages 210 in the direction of cold side 202 is thermallyisolated from the high magnetic field zones at magnets 230 in each ofthermal stages 210. Thus, thermal stages 210 are arranged to discouragethermal energy flow through thermal stages 210 from hot side 204 towardscold side 202 along the axial direction A during relative rotationbetween thermal stages 210 and magneto-caloric cylinder 220.

Magneto-caloric thermal diode 200 may include a suitable number ofthermal stages 210. For example, thermal stages 210 may include ninethermal stages as shown in FIGS. 3 and 4. In alternative exampleembodiments, thermal stages 210 may include no less than seven thermalstages. Such number of thermal stages 210 may advantageously permitmagneto-caloric cylinder 220 to include a corresponding number of zoneswith different magneto-caloric materials and thereby allowmagneto-caloric thermal diode 200 to operate over a wide range ofambient temperatures as discussed above. Magneto-caloric thermal diode200 may have an odd number of thermal stages 210.

Each of magnets 230 in thermal stages 210 may be formed as a magnet pair236. One of magnet pair 236 may be mounted to or positioned at innersection 206 of each thermal stage 210, and the other of magnet pair 236may be mounted to or positioned at outer section 208 of each thermalstage 210. Thus, magneto-caloric cylinder 220 may be positioned betweenthe magnets of magnet pair 236 along the radial direction Ratcylindrical slot 211. A positive pole of one of magnet pair 236 and anegative pole of other of magnet pair 236 may face magneto-caloriccylinder 220 along the radial direction R at cylindrical slot 211.

Cylindrical slot 211 may be suitably sized relative to magneto-caloriccylinder 220 to facilitate efficient heat transfer between thermalstages 210 and magneto-caloric cylinder 220. For example, cylindricalslot 211 may have a width W along the radial direction R, andmagneto-caloric cylinder 220 may having a thickness T along the radialdirection R within cylindrical slot 211. The width W of cylindrical slot211 may no more than five hundredths of an inch (0.05″) greater than thethickness T of magneto-caloric cylinder 220 in certain exampleembodiments. For example, the width W of cylindrical slot 211 may aboutone hundredth of an inch (0.01″) greater than the thickness T ofmagneto-caloric cylinder 220 in certain example embodiments. As usedherein, the term “about” means within five thousandths of an inch(0.005″) when used in the context of radial thicknesses and widths. Suchsizing of cylindrical slot 211 relative to magneto-caloric cylinder 220can facilitate efficient heat transfer between thermal stages 210 andmagneto-caloric cylinder 220.

Each thermal stage 210 may include a suitable number of magnets 230. Forexample, each thermal stage 210 may include no less than ten (10)magnets 230 in certain example embodiments. With such a number ofmagnets 230, may advantageously improve performance of magneto-caloricthermal diode 200, e.g., by driving a larger temperature differencebetween cold side 202 and hot side 204 relative to a smaller number ofmagnets 230.

Magnets 230 may also be uniformly spaced apart along the circumferentialdirection C within the non-magnetic ring 240 in each of thermal stages210. Further, each of thermal stages 210 may be positioned at a commonorientation with every other one of thermal stages 210 within the stackof thermal stages 210. Thus, e.g., first one 217 of interior thermalstages 216 may be positioned at a common orientation with third one 219of interior thermal stages 216, and hot side thermal stage 214 may bepositioned at a common orientation with second one 218 of interiorthermal stages 216. As may be seen from the above, the commonorientation may sequentially skip one thermal stage 214 with the stackof thermal stages 210. Between adjacent thermal stages 210 within thestack of thermal stages 210, each magnet 230 of thermal stages 210 maybe positioned equidistance along the circumferential direction C from arespective pair of magnets 230 in adjacent thermal stages 210.

The non-magnetic rings 240 of thermal stage 210 may be constructed of orwith a suitable non-magnetic material. For example, the non-magneticrings 240 of thermal stage 210 may be constructed of or with aluminum incertain example embodiments. In alternative example embodiments, thenon-magnetic rings 240 of thermal stage 210 may be constructed of orwith brass, bronze, etc.

Magneto-caloric thermal diode 200 may also include one or more heatexchangers 260. In FIG. 3, heat exchanger 260 is shown positioned at thecold side 202 such that heat exchanger 260 absorbs heat from cold sidethermal stage 212. A heat transfer fluid may flow between heat exchanger260 and cold side heat exchanger 32 via lines 44, 46 as discussed above.Another heat exchanger may be positioned hot side 204 such that a heattransfer fluid may flow between the heat exchanger and hot side heatexchanger 34 via lines 48, 50 as discussed above. The heat exchangers(including heat exchanger 260) may be solid-liquid heat exchangers witha port for heat transfer fluid. Alternatively, the heat exchangers couldbe direct to solid-gas heat exchangers.

FIG. 9 is a schematic view of the certain components of amagneto-caloric thermal diode 300 according to another exampleembodiment of the present subject matter. As shown in FIG. 9,magneto-caloric thermal diode 300 includes numerous common componentswith magneto-caloric thermal diode 200. Thus, the description ofmagneto-caloric thermal diode 200 provided above is applicable tomagneto-caloric thermal diode 300 except as otherwise noted. Inaddition, magneto-caloric thermal diode 200 may include one or more ofthe aspects of magneto-caloric thermal diode 300 discussed below.

In magneto-caloric thermal diode 300, magneto-caloric cylinder 220includes a plurality of magneto-caloric stages 222. Magneto-caloricstages 222 are distributed along the axial direction A withinmagneto-caloric cylinder 220. Each of magneto-caloric stages 222 mayhave a different magneto-caloric material. For example, the respectivemagneto-caloric material within each of magneto-caloric stages 222 maybe selected such that the Currie temperature of the magneto-caloricmaterials decreases from hot side 204 to cold side 202 along the axialdirection A. In such a manner, a cascade of magneto-caloric materialsmay be formed within magneto-caloric cylinder 220 along the axialdirection A.

Each of magneto-caloric stages 222 may also have a respective lengthalong the axial direction A. In particular, a length LM1 of a first one224 of magneto-caloric stages 222 may be different than the length LM2of a second one 226 of magneto-caloric stages 222. It will be understoodthat each magneto-caloric stage 222 may have a different length in themanner described above for first one 224 and second one 226 ofmagneto-caloric stages 222 in certain example embodiments. However, inalternative example embodiments, one or more of magneto-caloric stages222 may have a common length with first one 224 or second one 226 ofmagneto-caloric stages 222.

Each of thermal stages 210 also having a respective length along theaxial direction A. The length of each of thermal stages 210 correspondsto a respective one of magneto-caloric stages 222. Thus, each of thermalstages 210 may be sized to match the respective one of magneto-caloricstages 222 along the axial direction A. The respective one ofmagneto-caloric stages 222 is disposed with each thermal stage 210.

The length of each of magneto-caloric stages 222 along the axialdirection A may be selected to assist with matching heat transfer power,e.g., such that each of magneto-caloric stages 222 accepts heat to oneadjacent magneto-caloric stage 222 and rejects heat to the otheradjacent magneto-caloric stage 222 along the axial direction A. Withineach magneto-caloric stage 222, the rejected heat may be slightly morethan the accepted heat based on stage efficiency, and the length of eachof magneto-caloric stages 222 along the axial direction A may beselected to complement the efficiency of each magneto-caloric stage 222.

As an example, the length of each of magneto-caloric stages 222 maycorrespond to a respective Curie temperature spacing between adjacentmagneto-caloric stages 222. In particular, the Curie temperature spacingfor the first one 224 of magneto-caloric stages 222 may be greater thanthe Curie temperature spacing for the second one 226 of magneto-caloricstages 222. Thus, the length LM1 of first one 224 of magneto-caloricstages 222 may be greater than the length of LM2 of second one 226 ofmagneto-caloric stages 222, e.g., in proportion to the differencebetween the Curie temperature spacing. As may be seen from the above,magneto-caloric stages 222 with larger Curie temperature spacing betweenadjacent magneto-caloric stages 222 may advantageously have an increasedlength along the axial direction A relative to magneto-caloric stages222 with smaller Curie temperature spacing between adjacentmagneto-caloric stages 222.

As another example, the length of each of magneto-caloric stages 222 maycorrespond to an adiabatic temperature change (i.e., the strength) ofthe magneto-caloric stage 222. In particular, the adiabatic temperaturechange of the first one 224 of magneto-caloric stages 222 may be lessthan the adiabatic temperature change of the second one 226 ofmagneto-caloric stages 222. Thus, the length LM1 of first one 224 ofmagneto-caloric stages 222 may be greater than the length of LM2 ofsecond one 226 of magneto-caloric stages 222, e.g., in proportion to thedifference between the adiabatic temperature changes. As may be seenfrom the above, weaker magneto-caloric stages 222 may advantageouslyhave an increased length along the axial direction A relative tostronger magneto-caloric stages 222.

As an additional example, the length of hot side thermal stage 214 alongthe axial direction A may be greater than the length of cold sidethermal stage 212 along the axial direction A. Thus, magneto-caloricstages 222 at or adjacent hot side 204 may be longer along the axialdirection A relative to magneto-caloric stages 222 at or adjacent coldside 202. In such a manner, magneto-caloric thermal diode 300 mayadvantageously configured to account for losses in magneto-caloricstages 222, e.g., where rejected heat is greater than accepted heat.

Magneto-caloric thermal diode 300 also includes multiple magneto-caloriccylinders 220 and multiple stacks of thermal stages 210 nestedconcentrically within each other. In particular, magneto-caloric thermaldiode 300 includes a first magneto-caloric cylinder 310 and a secondmagneto-caloric cylinder 312. Second magneto-caloric cylinder 312 ispositioned within first magneto-caloric cylinder 310 along the radialdirection R. Magneto-caloric thermal diode 300 also includes a firstplurality of thermal stages 320 and a second plurality of thermal stages322. First thermal stages 320 are stacked along the axial direction Abetween cold side 202 and hot side 204. Second thermal stages 322 arealso stacked along the axial direction A between cold side 202 and hotside 204. First thermal stages 320 are positioned within second thermalstages 322 along the radial direction R.

First and second thermal stages 320, 322 and first and secondmagneto-caloric cylinders 310, 312 are configured for relative rotationbetween first and second thermal stages 320, 322 and first and secondmagneto-caloric cylinders 310, 312. First and second thermal stages 320,322 and first and second magneto-caloric cylinders 310, 312 may beconfigured for relative rotation about the axis X that is parallel tothe axial direction A. As an example, first and second magneto-caloriccylinders 310, 312 may be coupled to motor 26 such that first and secondmagneto-caloric cylinders 310, 312 are rotatable relative to first andsecond thermal stages 320, 322 about the axis X with motor 26. Inalternative exemplary embodiments, first and second thermal stages 320,322 may be coupled to motor 26 such that first and second thermal stages320, 322 are rotatable relative to first and second magneto-caloriccylinders 310, 312 about the axis X with motor 26.

First thermal stages 320 define a first cylindrical slot 324, and firstmagneto-caloric cylinder 310 is received within first cylindrical slot324. Second thermal stages 322 define a second cylindrical slot 326, andsecond magneto-caloric cylinder 312 is received within secondcylindrical slot 326. Second cylindrical slot 326 is positioned inwardof first cylindrical slot 324 along the radial direction R.

First magneto-caloric cylinder 310 and first thermal stages 320 operatein the manner described above for thermal stages 210 and magneto-caloriccylinder 220 to transfer thermal energy along the axial direction A fromcold side 202 to hot side 204. Similarly, second magneto-caloriccylinder 312 and second thermal stages 322 also operate in the mannerdescribed above for thermal stages 210 and magneto-caloric cylinder 220to transfer thermal energy along the axial direction A from cold side202 to hot side 204.

Second magneto-caloric cylinder 312 and second thermal stages 322 arenested concentrically within first magneto-caloric cylinder 310 andfirst thermal stages 320. In such a manner, magneto-caloric thermaldiode 300 may include components for operating as multiplemagneto-caloric thermal diodes 200 nested concentrically. First andsecond magneto-caloric cylinders 310, 312 may have identical cascades ofmagneto-caloric materials along the axial direction A. Thus, e.g., firstand second magneto-caloric cylinders 310, 312 may have identicalmagneto-caloric materials along the radial direction R. By nestingsecond thermal stage 322 concentrically within first thermal stage 320,a total cooling power of magneto-caloric thermal diode 300 may beincreased relative to non-nested magneto-caloric thermal diodes.

First and second thermal stages 320, 322 may be arranged to provide aflow path for thermal energy along the axial direction A from cold side202 to hot side 204 of magneto-caloric thermal diode 300 in the mannerdescribed above for magneto-caloric thermal diode 200. For example, eachof first thermal stages 320 includes magnets 230 and non-magnetic ring240, and each of second thermal stages 322 includes magnets 230 andnon-magnetic ring 240. Magnets 230 and non-magnetic ring 240 may bearranged within first thermal stages 320 in the manner described abovefor magnets 230 and non-magnetic ring 240 of magneto-caloric thermaldiode 200. Magnets 230 and non-magnetic ring 240 may also be arrangedwithin second thermal stages 322 in the manner described above formagnets 230 and non-magnetic ring 240 of magneto-caloric thermal diode200.

Each non-magnetic ring 240 within first thermal stages 320 may be inconductive thermal contact with a respective non-magnetic ring 240within second thermal stages 322 along the radial direction R. Forexample, each non-magnetic ring 240 within first thermal stages 320 maybe integral (e.g., at least partially formed from a single piece ofmaterial) with the respective non-magnetic ring 240 within secondthermal stages 322 along the radial direction R. By placing eachnon-magnetic ring 240 within first thermal stages 320 in conductivethermal contact with the respective non-magnetic ring 240 within secondthermal stages 322, thermal energy flow along the radial direction Rbetween first and second thermal stages 320, 322.

FIG. 10 is a schematic view of the certain components of amagneto-caloric thermal diode 400 according to an additional exampleembodiment of the present subject matter. As shown in FIG. 10,magneto-caloric thermal diode 400 includes numerous common componentswith magneto-caloric thermal diodes 200, 300. Thus, the description ofmagneto-caloric thermal diodes 200, 300 provided above is applicable tomagneto-caloric thermal diode 400 except as otherwise noted. Inaddition, magneto-caloric thermal diodes 200, 300 may include one ormore of the aspects of magneto-caloric thermal diode 400 discussedbelow.

Like magneto-caloric thermal diode 300, magneto-caloric thermal diode400 includes multiple magneto-caloric cylinders 220 and multiple stacksof thermal stages 210 nested concentrically within each other. Inparticular, magneto-caloric thermal diode 400 includes a firstmagneto-caloric cylinder 410 and a second magneto-caloric cylinder 412.Second magneto-caloric cylinder 412 is positioned within firstmagneto-caloric cylinder 410 along the radial direction R.Magneto-caloric thermal diode 400 also includes a first plurality ofthermal stages 420 and a second plurality of thermal stages 422. Firstthermal stages 420 are stacked along the axial direction A between coldside 202 and hot side 204. Second thermal stages 422 are also stackedalong the axial direction A between cold side 202 and hot side 204.First thermal stages 420 are positioned within second thermal stages 422along the radial direction R. First and second thermal stages 420, 422and first and second magneto-caloric cylinders 410, 412 are configuredfor relative rotation between first and second thermal stages 420, 422and first and second magneto-caloric cylinders 410, 412.

Second magneto-caloric cylinder 412 and second thermal stages 422 arenested concentrically within first magneto-caloric cylinder 410 andfirst thermal stages 420. In such a manner, magneto-caloric thermaldiode 400 may include components for operating as multiplemagneto-caloric thermal diodes 200 nested concentrically. First andsecond magneto-caloric cylinders 410, 412 may have different cascades ofmagneto-caloric materials along the axial direction A. Thus, e.g., firstand second magneto-caloric cylinders 410, 412 may have differentmagneto-caloric materials along the radial direction R. By nestingsecond thermal stage 422 concentrically within first thermal stage 420,a total temperature span of magneto-caloric thermal diode 400 relativeto non-nested magneto-caloric thermal diodes.

First and second thermal stages 420, 422 may be arranged to provide aflow path for thermal energy along the axial direction A from cold side202 to hot side 204 of magneto-caloric thermal diode 400 in the mannerdescribed above for magneto-caloric thermal diode 200. For example, eachof first thermal stages 420 includes magnets 230 and non-magnetic ring240, and each of second thermal stages 422 includes magnets 230 andnon-magnetic ring 240. Magnets 230 and non-magnetic ring 240 may bearranged within first thermal stages 420 in the manner described abovefor magnets 230 and non-magnetic ring 240 of magneto-caloric thermaldiode 200. Magnets 230 and non-magnetic ring 240 may also be arrangedwithin second thermal stages 422 in a similar manner to that describedabove for magnets 230 and non-magnetic ring 240 of magneto-caloricthermal diode 200 except that the arrangement of second thermal stage422 may be reversed along the axial direction A.

In addition, the non-magnetic ring 240 in the one of first thermalstages 420 at cold side 202 may be in conductive thermal contact withthe non-magnetic ring 240 in the one of second thermal stages 422 atcold side 202 along the radial direction R. For example, thenon-magnetic ring 240 in the one of first thermal stages 420 at coldside 202 may be integral (e.g., at least partially formed from a singlepiece of material) with the one of second thermal stages 422 at coldside 202 along the radial direction R. By placing the non-magnetic ring240 in the one of first thermal stages 420 at cold side 202 inconductive thermal contact with the one of second thermal stages 422 atcold side 202, thermal energy flow along the radial direction R betweenfirst and second thermal stages 420, 422 at cold side 202.

Other than at cold side 202, each non-magnetic ring 240 in first thermalstages 420 may be spaced from a respective non-magnetic ring 240 insecond thermal stages 422 along the radial direction R. For example,other than at cold side 202, each non-magnetic ring 240 in first thermalstages 420 may be spaced from the respective non-magnetic ring 240 insecond thermal stages 422 along the radial direction R by insulation430. By spacing each non-magnetic ring 240 in first thermal stages 420from the respective non-magnetic ring 240 in second thermal stages 422other than at cold side 202, thermal energy flow along the radialdirection R between first and second thermal stages 420, 422 may belimited.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A magneto-caloric thermal diode assembly,comprising: a magneto-caloric cylinder; and a plurality of thermalstages stacked along an axial direction between a cold side and a hotside, a cold side thermal stage of the plurality of thermal stagespositioned at the cold side, a hot side thermal stage of the pluralityof thermal stages positioned at the hot side, each of the plurality ofthermal stages comprising a plurality of magnets and a non-magneticring, the plurality of magnets distributed along a circumferentialdirection within the non-magnetic ring in each of the plurality ofthermal stages; wherein the plurality of thermal stages and themagneto-caloric cylinder are configured for relative rotation betweenthe plurality of thermal stages and the magneto-caloric cylinder, eachof the plurality of thermal stages between the cold side thermal stageand the hot side thermal stage is positioned between a respective pairof the plurality of thermal stages along the axial direction, one of therespective pair of the plurality of thermal stages is positioned closerto the cold side along the axial direction, the other of the respectivepair of the plurality of thermal stages is positioned closer to the hotside along the axial direction, the plurality of magnets of each of theplurality of thermal stages between the cold side thermal stage and thehot side thermal stage is spaced from the non-magnetic ring of the oneof the respective pair of the plurality of thermal stages along theaxial direction, and the plurality of magnets of each of the pluralityof thermal stages between the cold side thermal stage and the hot sidethermal stage is in conductive thermal contact with the non-magneticring of the other of the respective pair of the plurality of thermalstages.
 2. The magneto-caloric thermal diode assembly of claim 1,wherein each of the plurality of magnets comprises a magnet pair, themagneto-caloric cylinder positioned between the magnets of the magnetpair along a radial direction.
 3. The magneto-caloric thermal diodeassembly of claim 2, wherein a positive pole of one of the magnet pairand a negative pole of other of the magnet pair face the magneto-caloriccylinder along the radial direction.
 4. The magneto-caloric thermaldiode assembly of claim 1, wherein the plurality of magnets of each ofthe plurality of thermal stages between the cold side thermal stage andthe hot side thermal stage is spaced from the non-magnetic ring of theone of the respective pair of the plurality of thermal stages along theaxial direction by insulation.
 5. The magneto-caloric thermal diodeassembly of claim 1, further comprising a heat exchanger positioned atthe cold side.
 6. The magneto-caloric thermal diode assembly of claim 1,wherein the plurality of magnets is spaced from the non-magnetic ringalong the radial direction and the circumferential direction within eachof the plurality of thermal stages.
 7. The magneto-caloric thermal diodeassembly of claim 6, wherein each of the plurality of thermal stagesfurther comprises insulation positioned between the plurality of magnetsand the non-magnetic ring along the radial direction and thecircumferential direction.
 8. The magneto-caloric thermal diode assemblyof claim 1, wherein the non-magnetic ring is an aluminum ring.
 9. Themagneto-caloric thermal diode assembly of claim 1, wherein the pluralityof magnets are uniformly spaced apart along the circumferentialdirection within the non-magnetic ring in each of the plurality ofthermal stages.
 10. The magneto-caloric thermal diode assembly of claim9, wherein each of the plurality of thermal stages comprises no lessthan ten magnets.
 11. The magneto-caloric thermal diode assembly ofclaim 1, wherein the plurality of thermal stages and the magneto-caloriccylinder are configured for relative rotation about an axis that isparallel to the axial direction.
 12. The magneto-caloric thermal diodeassembly of claim 1, wherein the plurality of magnets and thenon-magnetic ring of each of the plurality of thermal stagescollectively define a cylindrical slot, the magneto-caloric cylinderpositioned within the cylindrical slot.
 13. The magneto-caloric thermaldiode assembly of claim 12, wherein the cylindrical slot has a widthalong a radial direction, the magneto-caloric cylinder having athickness along the radial direction within the cylindrical slot, thewidth of the cylindrical slot being no more than one hundredth of aninch greater than the thickness of the magneto-caloric cylinder.
 14. Themagneto-caloric thermal diode assembly of claim 1, wherein the pluralityof thermal stages comprises no less than seven thermal stages.
 15. Amagneto-caloric thermal diode assembly, comprising: a plurality ofthermal stages stacked along an axial direction between a cold side anda hot side, a cold side thermal stage of the plurality of thermal stagespositioned at the cold side, a hot side thermal stage of the pluralityof thermal stages positioned at the hot side, each of the plurality ofthermal stages comprising a plurality of magnets and a non-magneticring, the plurality of magnets distributed along a circumferentialdirection within the non-magnetic ring in each of the plurality ofthermal stages wherein each of the plurality of thermal stages betweenthe cold side thermal stage and the hot side thermal stage is positionedbetween a respective pair of the plurality of thermal stages along theaxial direction, one of the respective pair of the plurality of thermalstages is positioned closer to the cold side along the axial direction,the other of the respective pair of the plurality of thermal stages ispositioned closer to the hot side along the axial direction, theplurality of magnets of each of the plurality of thermal stages betweenthe cold side thermal stage and the hot side thermal stage is spacedfrom the non-magnetic ring of the one of the respective pair of theplurality of thermal stages along the axial direction, and the pluralityof magnets of each of the plurality of thermal stages between the coldside thermal stage and the hot side thermal stage is in conductivethermal contact with the non-magnetic ring of the other of therespective pair of the plurality of thermal stages.
 16. Themagneto-caloric thermal diode assembly of claim 15, wherein theplurality of magnets of each of the plurality of thermal stages betweenthe cold side thermal stage and the hot side thermal stage is spacedfrom the non-magnetic ring of the one of the respective pair of theplurality of thermal stages along the axial direction by insulation. 17.The magneto-caloric thermal diode assembly of claim 15, wherein theplurality of magnets is spaced from the non-magnetic ring along theradial direction and the circumferential direction within each of theplurality of thermal stages.
 18. The magneto-caloric thermal diodeassembly of claim 17, wherein each of the plurality of thermal stagesfurther comprises insulation positioned between the plurality of magnetsand the non-magnetic ring along the radial direction and thecircumferential direction.
 19. The magneto-caloric thermal diodeassembly of claim 15, wherein the plurality of magnets are uniformlyspaced apart along the circumferential direction within the non-magneticring in each of the plurality of thermal stages.
 20. A magneto-caloricthermal diode assembly, comprising: a magneto-caloric cylinder; and aplurality of thermal stages stacked along an axial direction between acold side and a hot side, a cold side thermal stage of the plurality ofthermal stages positioned at the cold side, a hot side thermal stage ofthe plurality of thermal stages positioned at the hot side, each of theplurality of thermal stages comprising a plurality of non-magneticblocks and a magnetic ring, the plurality of non-magnetic blocksdistributed along a circumferential direction within the magnetic ringin each of the plurality of thermal stages; wherein the plurality ofthermal stages and the magneto-caloric cylinder are configured forrelative rotation between the plurality of thermal stages and themagneto-caloric cylinder, each of the plurality of thermal stagesbetween the cold side thermal stage and the hot side thermal stage ispositioned between a respective pair of the plurality of thermal stagesalong the axial direction, one of the respective pair of the pluralityof thermal stages is positioned closer to the cold side along the axialdirection, the other of the respective pair of the plurality of thermalstages is positioned closer to the hot side along the axial direction,the plurality of non-magnetic blocks of each of the plurality of thermalstages between the cold side thermal stage and the hot side thermalstage is spaced from the magnetic ring of the one of the respective pairof the plurality of thermal stages along the axial direction, and theplurality of non-magnetic blocks of each of the plurality of thermalstages between the cold side thermal stage and the hot side thermalstage is in conductive thermal contact with the magnetic ring of theother of the respective pair of the plurality of thermal stages.